Servlet Specification

The Java Servlet Specification is a document that details the design and API of a Java-based system that can respond to requests.
To learn more about the specification itself, visit the link near the start of this paragraph.

Repose is built on top of the servlet specification.
However, Repose also constrains the specification in certain ways.
For example, Repose can only service HTTP requests.

To understand the architecture of Repose, it is vital that one understands the servlet specification.
Currently, Repose complies with version 3.0 of the specification.

Filter

The ReposeFilter class implements the Filter API and is the only filter in the base containers FilterChain.
It uses the ReposeFilterLoader class to load the FilterContext 's that are passed to the ReposeFilterChain.

Before calling into the Repose Filter Chain, it enhances the request from the client with a unique Transaction ID, if one is not already present, and starts a span with the OpenTracing Service.
When the Repose Filter Chain completes, the OpenTracing span is closed, the Via header is updated on the response, and the Metrics Service is updated.

Filter Chain

The ReposeFilterChain class implements the FilterChain API, and is responsible for the coordination between filters.
That coordination includes things like dynamic determination of whether or not a filter should process a request or response, debug logging, and metrics gathering.
To learn more about this component, visit the filter chain documentation page.

Servlet

The ReposeRoutingServlet class implements the Servlet API and is registered with the servlet container.
It is responsible for routing the HTTP request from Repose to the origin service after the filter chain has finished processing the request.

This servlet uses the configuration information stored in the System Model to determine what destinations are available.
Routing to an app on the same host but in another container or environment is easily configured in a generic way.

The preferred deployment strategy is to put a repose node as a side-car proxy on the same host as the origin service in a 1 to 1 fashion.
If Repose needs to horizontally scale at a different rate from the origin service, then putting an external load balancer as the destination is the safer option.